A liquid crystal display (LCD) typically includes a thin film transistor array panel, a color filter panel, and a liquid crystal layer sandwiched between the thin film transistor array and the color filter panel.
In this design, the thin film transistor array panel will generally include thin film transistors, pixel electrodes, gate lines and data lines. The color filter panel, on the other hand, will generally include color filters and a common electrode.
In operation, a gate electrode of a thin film transistor in the transistor array panel is supplied with a gate driving signal from a gate driver via a gate line which activates the thin film transistor. Therefore, a data signal applied to a source electrode of the thin film transistor from a data driver via a data line is supplied to the pixel electrode in order to switch the LCD pixel of the liquid crystal layer. In addition, the common electrode of the color filter panel is supplied with a common voltage through dummy pads of an out lead bonding (OLB) region and conductive members made of silver paste which are formed in the outer regions of the thin film transistor array panel. It is desirable that the paths through which the gate driving signals and common voltages pass have low resistivity in order to improve low voltage operation and reduced cross-talk. However, the paths of the common voltages encounter numerous resistances such as the contact resistance of the dummy pads, the resistance of the dummy pads themselves, the contact resistance of a common voltage driving circuit, the contact resistance of the conductive members connecting the dummy pads and the common electrode, and the resistance of the common electrode which is typically made of indium-tin-oxide (ITO). Several of these resistances are discussed in more detail below with reference to FIG. 1 which shows a cross-sectional view of a voltage transfer circuit from an OLB pad region to a short region that is connected to a common electrode.
In FIG. 1, a thin film transistor array panel includes a lower substrate 1 on which a gate insulating layer 3 is formed. A metal layer 5 which is connected to a data line is formed on the insulating layer 3. The metal layer 5 is typically made of chromium (Cr). A passivation layer 7 with two holes is formed on the metal layer 5, and an ITO layer 9 is formed thereover and connected to the metal layer 5 through the two holes. The thin film transistor array panel includes a dummy pad region B for receiving the external or common voltage and a short region A where a conductive member 11 electrically connects the thin film transistor array panel to the color filter panel. The color filter panel includes an upper substrate 19 covering a black matrix 13. Adjacent to the black matrix 13 is an overcoat layer 15. In addition, a common electrode 17 which is typically made of ITO is formed over the common electrode 17. Accordingly, the conductive member 11 contacts the ITO layer 9 of the thin film transistor array panel at the short region A and the common electrode 17 of the color filter panel, as shown.
When a common voltage supply from the common voltage driving circuit is applied to the dummy pad region B, the resulting voltage at the common electrode 17 is less than the applied common voltage because of the resistance in the pad region B having the structure of insulator/Cr/ITO layers, the resistance in the short region A having the structure of insulator/Cr/ITO layers, the resistance in a central region between the pad region B and the short region A having the structure of insulator/Cr/passivation/ITO layers, and the resistance in the conductive member 11. In particular, it is noted that the resistivity in the pad region B is relatively large due to its structure of the Cr/ITO layers. Further, the resistance from the center region to the short region A is relatively large due to the large resistivity of the chromium comprising the metal layer 5. As a result of the resistance to the common voltage, an increase in cross-talk may occur in the liquid crystal display. Thus, it would be desirable to be able to reduce the resistivity to the common voltage applied in order to reduce the presence of cross-talk in the LCD.